Document US 2008/0077020 A1 describes a method and an apparatus for monitoring vital signs, such as cardiopulmonary activity, using a ballistograph. The method and the apparatus are used to monitor an infant sleeping in a crib, a patient in a hospital, a person with a chronic disease at home or in professional care, or a person in an elder-care setting.
Heart activity is one of the most important vital life signs for a human or an animal. In the following, a subject comprises a human, such as a baby or a neonate, and an animal. In this description, neonates are focused on. However, the idea of the invention is applicable to all humans or animals. The heart rate, HR for short, and also the heart rate variation or heart rate variability, HRV for short, have become a topic of interest in physiology and in psychology. Both values are of particular interest to monitor vital life signs. HRV is attributed to the balance between the parasympathetic nervous system and the sympathetic nervous system, PNS and SNS for short, respectively decreasing and increasing the HR.
The principle of a ballistographic method is based on a motion sensor, placed or positioned under a mattress of a lying person for monitoring the movements of that person, in particular in the vertical direction relative to the fixed ground.
However, the use of the ballistographic method is problematic due to the fact that such a method mainly measures forces oriented in a vertical direction relative to the ground. However, the force due to the aortic arch impulse in a subject's body, preferably a human's body, is mainly oriented in a horizontal direction relative to the ground.
Besides the ballistographic method, the use of electrodes is known as well. This alternative of measuring heart activity by electrodes is obtrusive, in particular for the neonate, the baby or the child, because the child must be easily forwarded to its parents in order to improve the parent child contact or the child must be easily accessible for care givers, for instance for doctors or nurses working in a hospital. It goes without saying that the skin of the child is very thin and fragile, and may be damaged by removing the electrodes. On the other hand, such a system is robust and able to detect HR among disturbing movement artifacts and the system is for hygienic reasons easy to maintain.
Nevertheless, there is a need for overcoming the problems of the prior art, in particular when measuring HR or HRV of neonates.